Synchronization of camera and television receiver tube



c. D. MAURER ETAL. SYNCHRONIZATION 0F CAMERA AND Nov. 1, 1949 TELEVIS ION RECEIVER TUBES 2 sheets-sheet 1 Filed March 20, 1946 mmDP )qm NDOIICQU lll JHI INVENTORS CARL D. MAURER WALTER J. SWENSON BY 'AQ Tx 1 .drmf

ATT RNEY NOV- l 1949 c. D. MAURER ET AL 2,486,717

SYNCHRONIZATION OF CAMERA AND TELEVISION RECEIVER TUBES Filed March 20, 1946 2 Sheets-Sheet 2 FULL wAvE REcTlFlER uuLTlvleRAToR POWER LINE FR EQ U NGY INVENTOR. CARL D. MAURER BY WALTER J. swENsoN 4&7 v

ATT NEYS Patented Nov. 1, 1949 UNITED STAT ES PATENT OFFICE SYNCHRONIZATION OF CAMERA AND TELEVISION RECEIVER TUBE ration of New York Application March 20, 1946, Serial No. 655,652 I z claims. (c1. 11s-7.4)

It is desirable to be able to photograph the picture which appears on the screen of a television receiver. One reason Why this is desirable is that a full record may be made and kept of programs transmitted in case of later controvery with respect to them. Of course, it is possible to use a motion picture camera and sound recording equipment to make a record directly from the scene being transmitted, but the camera in such a case might not always record `exactly what was transmitted over the air due to the difference in angle, etc., and in transmitting outdoor scenes such as sports events it might at times be inconvenient or impossible to use a photographic kcamera simultaneously with the television pick-up mechanism.

Another important reason why it is desirable to make such a photograph is that it provides a means for projecting a television scene upon the large screen-of a motion picture theatre with sumcient picture quality as to be regularly acceptable to paying patrons. For example, a sports event might occur in one city, be picked up and transmittedby television to another lo- 'cation in the same or another city, received at a motion picture theatre where the television receiver screen is photographed, the lm developed and immediately yprojected upon the screen for a large audience.

It is highly desirable to be able to use standard motion picture equipment for photographing a television screen. Perhaps the most important reasons for this are that such equipment has been carefully developed over along period of years so that it is thoroughly reliable audits operation well understood by large numbers of people, that it operates on standards as to frame frequency, etc., which are widely applicable throughout 'the world, and that it is of course cheaper and more satisfactory to use existing equipment than to develop something new. Perhaps the most important reason is in connection with prompt reshowing of the scene upon a motion picture screen Where theiilm if produced in accordance with standard motion picture practice, may then be immediately used in a standard motion picture projector.

In accordance with present television standards, television signals are transmitted at 525.

lines per frame with a frame frequency of 30 frames per second and a 2 to 1 interlace, giving a eld frequency of 60 elds per second.

Present motion picture standards involve the photographing and projecting of motion picturesat a frame frequency of 24 per second.

' ance with the present standards:

Figure 2 is an illustration of the characteristics of a motion picture camera; and

Figure 3 is an illustration coupled with a block diagram of the method and means employed in the present invention.

Figure 4 is a schematic or circuit diagram of the electronic circuits shown in block form in Figure 3.

Referring rst to Figure l, it is there illustrated that the time between the start of two successive frames of a television signal transmitted in accordance with present standards is 4/120 of a second 'and the time between two suc'- cessive elds is 2/,120 of a second.

Figure 2 is drawn to the same time scale as Figure l and illustrates the fact that in a motion picture camera the lm moves from frame to frame during an interval of approximately 1/120 of a second and is stationary for an interval of approximately 4/120 of a second, so that the time between frame is 5/1720 or 1/24 of a second.

It is possible to use a standard motion picture camera to photograph a Atelevision screen without any special equipment or precautions and thereby obtain a'iilm record. Such a nlm, however, will exhibit certain aberrations and will not be of good enough quality for use for projection purposes in a motion picture theatre. The rreasons for this may be understood by referring to Figures 1 and 2.

Let us assume that the shutter opening of the camera is set for 4/120 of a second so that it is open during the entire period that the film is stationary for any frame, 'and that the phase of operation of the camera and television picture is as indicated in Figures 1 and 2. That is, that the lm stops and the shutter opens exactly 1/izo of 'a second after the beginning of a television frame for Ithe rst lm frame, and thereafter at corresponding periods as illustrated in these two4 gures.

N it will show on the screen before the caxxral camera will therefore miss the second half of the first field of frame number 2. However, it will record the entire second field of the second frame and the entire first field of the third frame so that it will again record an entire frame. The film then will move again and the shutter be closed during the next 1/izo of a second so that it will miss the first half of the second eld of the third frame of the television picture. The shutter 'will be open, however, for the second half of the second field of this frame, for the rst eld of the fourth frame and for the first half of the second eld of the fourth frame, again recording one entire frame. The camera film will again move for 1/120 of a second while the shutter is closed and will reopen with the beginning of the fth frame so that it will record the entire fifth television frame. At this point it will be noted that the phase of camera lin and television frame is the saine as at frame number I so that it will be obvious that succeeding frames of film and pictures will be the same as those just described.

As stated, the picture taken on the film will be one which will be a record of the picture appearing on the television screen. It will not, however, be a good one because of the mechanical variations of the camera shutter. That is, in order to have a good film record the synchronization between the camera shutter and the television frame must be perfect and lthe shutter opening must be exact. While the foregoing has been described in terms of securing a picture -of exactly one full television frame during each shutter opening actually this will not occur due to these mechanical variations. As one line of a Atelevision picture occurs in approximately 64 -microseconds the action of the camera shutter must be accurate within only a few microseconds in order to obtain a uniformly good result. Such mechanical accuracy is extremely difficult and if it may be achieved at all would be inordinately expensive.

If the camera shutter action is not accurate to this extent it will record on the lm something more or less than exactly one frame of the television picture. The result of this is that if the shutter is open too long by, say 64 microseconds, one line of the television picture will be scanned twice while the shutter is open and a clark line will appear across the iilm at this point. If the shutter is open too short a time by, for example, 64 microseconds a light line will appear across the picture, where this line is not scanned during the open shutter period. Such lines are very noticeable and would be highly objectionable in a theatre projection.

Figure 3 illustrates one exemplicationi of the method and apparatus which we have invented for avoiding the difficulties described above. We use a standard motion picture camera which is operated by a synchronized motor from any 60 cycle power line. From the same power line we develop a pulse which may be controlled in terms of a fraction of a microsecond which occurs A24 times per second and which is 1/120 of a s'econdin' duration, and use this pulse to blank gnam the television screen tube or kinescope, synchronously with the movement of the film in the camera. In addition to this we remove the shutter from the camera so that Ithe lm is exposed to the television screen at all times. We further use a television screen with short persistence luminescence which will be referred to later.

By actual test we have found that this method of operation gives us uniformly good pictures of a quality satisfactory for motion picture projection before a critical audience.

The apparatus illustrated in Figure .3 which we have found useful in practicing our invention, and which is simply illustrative of many different types of apparatus which might be used, includes a full wave rectifier I which is supplied With a voltage from a 6() cycle power line. The rectier I produces a 120 cycle wave from the i 60 cycle wave. It supplies a blocking oscillator 2 which produces 120 pulses per second from the cycle wave. These pulses are supplied to a multivibrator 3 which produces 24 square waves per second each having a duration of exactly 1/120 of a second. These square waves are supplied to the television tube or kinescope 4 to blank the tube during the duration of each square wave in a manner which will be well understood.

The camera 5 is driven by a synchronous motor from the same power line which supplies the rectifier I. By suitable mechanism such, for example, as a switch which opens and closes in series with a voltage source, the camera produces a series of synchronizing pulses which match those produced by the multivibrator 3. The pulses from the multivibrator and those from the camera may both be applied to a cathode ray tube for visual comparison and manual adjustment of the multivibrator for synchronism with the camera. 'I'his adjustment is Very simple and once made need not be repeated during the operation. It will be noted that the multivibrator 3 produces one square wave for each ve pulses, and the synchronizing problem involves only selecting which of the ve pulses it will follow. 'Ihis may be accomplished by allowing it to drift from the one to the other until it picks up the right one as shown by the cathode ray tube 6. Synchronism between the blanking wave and the camera operation will then be established, and as stated no further attention need be given to synchronization. Of course, it is possible to accomplish this synchronism automatically in a number of other ways well known to those skilled in the art and we are therefore simply illustrating one convenient way of accomplishing it manually.

A pulse from the camera could be used as a blanking pulse for the television screen, as one simple method of automatic synchronization.

It is to be noted that the blanking pulses supplied to the Itelevision tube from the multivibrator are derived fromthe local power line and not from the incoming television signal. The reason for this is that the camera will be operated from the'local power line and the blanking pulses must be in synchronism with the operation of the camera. They need not, however, be in synchionism with the television picture. That is,. we have illustrated in Figures 1 and 2 a phase of operation in which the lm begins to record at the beginning of every fourth lm frame and at the beginning of every fifth television frame in exact phase. These frames have been so illustrated for convenience of explanation. Actually, the

phase relationship between lm and television pictures is immaterial, the important factor being that the film be exposed for the exact duration of one television frame.

In order to practice our invention successfully it is further necessary to use a television tube having a short persistence screen. The reason for this is that there is no mechanical shutter in the camera and the film is exposed to the scene on the television screen at all times. Therefore, if this scene does not decay promptly after the blanking pulse from multivibrator 3 is applied to the television tube there will be enough light on the sceen to affect the film during the times the lm is moving from frame to frame. For satisfactory results, the decay characteristics of the screen will of course be related to the voltages used in the television tube, the screen material used, and also on the film and developer characteristics. We have found, however, that a screen is thoroughly satisfactory in which the light on the screen decays in 116 microseconds to of its maximum value when used with film having a degree of inertia which corresponds to the decay time of the screen material. The materials and method of producing a screen with .this characteristic are well known, as is such a While we have described the voperation of our invention as involving the nlm being stationary for 4/120 of a second, equal to the time of one television frame, and moving during 1/izo of a second, this being the remainder of the time available for one camera frame, actually the film may remain stationary for a slightly longer time,

in order to provide a safety factor from the standpoint of accuracy of mechanical movement with respect to time. This additional length of the stationary period will not effect the operation asthe television screen will be blanked out with the accuracy indicated except for the exact duration of one complete television frame. The safety factor permits the mechanical movement of the film without the precise timing required of a shutter where one is used with an attempt to have it open for the exact length of time of one television frame.

As explained above the camera 5 may be a standard motion picture camera, and if such a standard camera is used it will contain apparatus for recording sound on the film. The sound accompanying the television scene being photographed may therefore be supplied to the camera in the form of an electrical signal derived from the incoming complete television signal, and photographed upon the nlm in the form of a sound track in the usual manner. The film upon being developed will therefore contain the usual sound track for motion picture projection with accompanying sound by the use of the standard sound motion picture equipment found in most motion picture theatres.

It will be obvious to those skilled in the art that our invention is capable of various modications and we do not therefore desire to be re- 6 stricted lto the particular details shown and described but only within the scope of the appended claims.

What is claimed is:

1. Apparatus for photographing a scene appearing upon a television receiver which comprises a cathode ray tube, a 60 cycle power line, a full-wave rectifier connected thereto producing a cycle wave, a blocking oscillator connected to said rectifier to produce 120 pulses per second, 'a multivibrator connected to said blocking oscillator to produce 24 blanking pulses per second yeach having a duration of 1/120 second, a motion picture camera having no shutter, means for `applying said blanking pulses to the television receiver tube to blank it during .the movement of the film in the camera, means for driving said camera from said 60 cycle power line in synchronism therewith, and means for selecting the blanking pulses in synchronism with the movement of the film.

2. Apparatus for photographing a television image comprising a television tube for reproducing said image, a motion picture camera for photographing said image on said tube and a power supply for operating said tube and said camera, a rectier circuit connected to said power sup-v ply and to a rst electrical pulse generating circuit generating a series of consecutive pulses at a predetermined frequency, a second electrical pulse generating circuit connected to said first electrical pulse generating circuit and producing pulses at the frame frequency rate of said camera, said second pulse generating circuit being selectively triggered by said `first pulse generating circuit, said second pulse generating circuit being connected to said television tube to control the on and off time of the image produced by said tube and a monitoring tube connected to said second pulse generating circuit and said camera for comparing the timing of said camera and said second pulse generating circuit for synchronizing the off time of said image with the move- 'ment of the film in saidcamera.

CARL D. MAURER. WALTER J. SWENSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,251,786 `Epstein Aug. 5, 1941 2,373,114 Goldsmith, Jr Apr. 10, 1945 FOREIGN PATENTS Number Country Date 394,496 Great Britain June 29, 1933 OTHER -REFERENCES Photography of Cathode Ray Tube Traces, RCA Review, vol. VI, No. 2, October 1941, pages 234-244. 

